Animals (Kingdom Animalia)

Animalia comprises all multicellular, eukaryotic organisms commonly referred to as animals. Members of this kingdom are characterized by the absence of cell walls, heterotrophic modes of nutrition, and specialized tissues that enable movement, sensory perception, and complex behaviors. Most animals obtain energy by ingesting organic material and digesting it internally.

Organisms within Animalia exhibit a wide range of body plans, from simple, asymmetrical forms such as sponges (Porifera) to highly complex, bilaterally symmetrical organisms with advanced nervous systems, including mammals, birds, reptiles, amphibians, and fishes (Chordata). Reproduction is predominantly sexual, with development typically involving a blastula stage during early embryogenesis.

Animals occupy nearly every ecosystem on Earth, including terrestrial, freshwater, marine, and aerial environments. They play essential ecological roles as predators, herbivores, decomposers, and pollinators, contributing significantly to ecosystem stability and biodiversity.

The kingdom Animalia is traditionally divided into numerous phyla, such as Arthropoda, Mollusca, Annelida, Echinodermata, and Chordata, reflecting evolutionary relationships based on morphology, embryology, and molecular data.